Preparation of Polyorganoborosilazanes and Conversion into Ultra-High-Temperature Borosilicon Carbonitrides

Abstract

Polyorganoborosilazanes with a wide range of B/Si/C ratios were synthesized by co-ammonolysis of various organochlorosilanes and borontrichloride. By pyrolysis of SiMe₂Cl₂-based or SiHC₂H₅Cl₂-based polyorganoborosilazane with limited B/Si/C ratios in an inert atmosphere, amorphous borosilicon carbonitrides stable at 1880°C were prepared. The amorphous structure of borosilicon carbonitride was closely related to distributions of B-N bonds, substituent groups on Si atoms and contents of B and C atoms in the preceramic polymers. Three-dimensional BCN networks in the ceramics maintained amorphous structures up to higher temperatures. These prepared ceramics were not only thermally stable, but the oxidation resistance is also excellent at 1700°C in dry air and at 1500°C under reduced pressures.